Synthesis of 3′,4′-difluoro-3′-deoxyribonucleosides and its evaluation of the biological activities: Discovery of a novel type of anti-HCV agent 3′,4′-difluorocordycepin

Upon reacting 3′,4′-unsaturated cytosine (8 and 9) and adenine nucleosides (13 and 14) with XeF₂/BF₃·OEt₂, the respective novel 3′,4′-difluoro-3′-deoxyribofuranosyl nucleosides (10–12 and 15–18) could be obtained. Formation of anti-adducts (11, 16 and 18) revealed that the fluorination involved oxonium ions as incipient intermediates. TBDMS-protected 3′,4′-unsaturated adenosine provided the β-face adducts as sole stereoisomers whereas α-face-selectivity was observed with the TBDPS-protected adenosine 14. The evaluation of the novel 3′-deoxy-3′,4′-difluororibofuranosylcytosine-(19–21) and adenine nucleosides (22–25) against antitumor and antiviral activities revealed that 3′,4′-difluorocordycepin (24) was found to possess anti-HCV activity. The SI of 24 was comparable to that of the anti-HCV drug ribavirin. However, sofosbuvir, FDA-approved novel anti-HCV drug, showed better SI value. Our finding revealed that the introduction of the fluoro-substituent into the 4′-position of cordycepin derivatives decreased the cytotoxicity to the host cell with retention of the antiviral activity.     

Study on the interaction between 4-(1H-indol-3-yl)-2-(p-tolyl)quinazoline-3-oxide and human serum albumin

An organic small-molecular drug, 4-(1H-indol-3-yl)-2-(p-tolyl)quinazoline-3-oxide 1a was synthesized. It was employed to investigate the binding interaction and mechanism with human serum albumin (HSA). The experimental results indicated that the fluorescence quenching of HSA by 1a is a static quenching process and formation 1a-HSA complex. The site competition experiments revealed that the combination of 1a on HSA are hydrophobic interactions in the IIA domain and hydrogen bonds in IIIA domain of HSA, and the hydrophobic interactions of 1a on HSA are stronger than that of hydrogen bonds. These results were also confirmed by molecular docking theoretic analysis and ANS-hydrophobic fluorescent probe experiment. Synchronous fluorescence experiments showed that the polarity of HSA microenvironment was increase in the interaction process of 1a with HSA. The results of binding distance explored indicated that the combination distance between 1a and HSA is 3.63 nm, which is between 0.5R₀ and 1.5R₀, revealing the energy transfer between HSA and 1a is non-radiative. These results are very helpful for people to screen out high efficient indoloquinazoline drugs.     

Why did heterospory evolve?

The primitive land plant life cycle featured the production of spores of unimodal size, a condition called homospory. The evolution of bimodal size distributions with small male spores and large female spores, known as heterospory, was an innovation that occurred repeatedly in the history of land plants. The importance of desiccation‐resistant spores for colonization of the land is well known, but the adaptive value of heterospory has never been well established. It was an addition to a sexual life cycle that already involved male and female gametes. Its role as a precursor to the evolution of seeds has received much attention, but this is an evolutionary consequence of heterospory that cannot explain the transition from homospory to heterospory (and the lack of evolutionary reversal from heterospory to homospory). Enforced outcrossing of gametophytes has often been mentioned in connection to heterospory, but we review the shortcomings of this argument as an explanation of the selective advantage of heterospory. Few alternative arguments concerning the selective forces favouring heterospory have been proposed, a paucity of attention that is surprising given the importance of this innovation in land plant evolution. In this review we highlight two ideas that may lead us to a better understanding of why heterospory evolved. First, models of optimal resource allocation – an approach that has been used for decades in evolutionary ecology to help understand parental investment and other life‐history patterns – suggest that an evolutionary increase in spore size could reach a threshold at which small spores yielding small, sperm‐producing gametophytes would return greater fitness per unit of resource investment than would large spores and bisexual gametophytes. With the advent of such microspores, megaspores would evolve under frequency‐dependent selection. This argument can account for the appearance of heterospory in the Devonian, when increasingly tall and complex vegetative communities presented competitive conditions that made large spore size advantageous. Second, heterospory is analogous in many ways to anisogamy. Indeed, heterospory is a kind of re‐invention of anisogamy within the context of a sporophyte‐dominant land plant life cycle. The evolution of anisogamy has been the subject of important theoretical and empirical investigation. Recent work in this area suggests that mate‐encounter dynamics set up selective forces that can drive the evolution of anisogamy. We suggest that similar dispersal and mating dynamics could have underlain spore size differentiation. The two approaches offer predictions that are consistent with currently available data but could be tested far more thoroughly. We hope to re‐establish attention on this neglected aspect of plant evolutionary biology and suggest some paths for empirical investigation.     

A testis‐specific gene within a widely expressed gene: Contrasting evolutionary patterns of two differentially expressed mammalian proteins encoded by a single gene,CAMK4

Understanding the patterns of genetic variations within fertility‐related genes and the evolutionary forces that shape such variations is crucial in predicting the fitness landscapes of subsequent generations. This study reports distinct evolutionary features of two differentially expressed mammalian proteins [CaMKIV (Ca²⁺/calmodulin‐dependent protein kinase IV) and CaS (calspermin)] that are encoded by a single gene, CAMK4. The multifunctional CaMKIV, which is expressed in multiple tissues including testis and ovary, is evolving at a relatively low rate (0.46–0.64 × 10^?9 nucleotide substitutions/site/year), whereas the testis‐specific CaS gene, which is predominantly expressed in post‐meiotic cells, evolves at least three to four times faster (1.48–1.98 × 10^?9 substitutions/site/year). Concomitantly, maximum‐likelihood‐based selection analyses revealed that the ubiquitously expressed CaMKIV is constrained by intense purifying selection and, therefore, remained functionally highly conserved throughout the mammalian evolution, whereas the testis‐specific CaS gene is under strong positive selection. The substitution rates of different mammalian lineages within both genes are positively correlated with GC content, indicating the possible influence of GC‐biased gene conversion on the estimated substitution rates. The observation of such unusually high GC content of the CaS gene (≈74%), particularly in the lineage that comprises the bovine species, suggests the possible role of GC‐biased gene conversion in the evolution of CaS that mimics positive selection.     

Laetoli toes andAustralopithecus afarensis

The probable misfit between feet, particularly toes II–V, of 3.0-million-year-oldAustralopithecus afarensis from Hadar, Ethiopia, and the 3.5-million-year-old hominid footprints at Site G, Laetoli, Tanzania, casts doubt thatA. Afarensis made the Laetoli trails. We suggest that another species ofAustralopithecus or an anonymous genus of the Hominidae, with remarkably humanoid feet, walked at Laetoli. It would be imprudent to declare thatHomo was present at Laetoli 3.5 million years ago (my) because there is no evidence of brain expansion, advanced tool manufacture, or other non-locomotor hallmarks of the human condition at Site G.     

The origin of homeostasis in the early earth

Summary An equation is developed that describes the condition of homeostasis in a general molecular system containing catalysts. In a prebiotic environment, this condition first results from a critical level of catalytic feedback in feedback loops containing differing organic molecular species. This critical level results in temporary exponential growth in concentrations of those catalyst species participating in the feedback loops, leading to homeostasis as the steady-state endpoint. None of the molecules in any feedback loop need be self-replicating for this autocatalysis to occur. Homeostasis is regarded as a definition of life at the lowest possible hierarchical level. A general mathematical boundary condition is derived for the critical level of catalytic feedback mentioned above-in effect, an origin of life condition. The paper argues that any natural prebiotic system of organic molecules in an H₂O medium will automatically form many catalytic feedback loops, even if of very low catalytic efficiency. The analysis in this paper indicates that high temperatures strongly increase the efficiency of such catalytic feedback. If the temperature and total concentration of carbon in the system (e.g., in CO₂, CH₄, etc.) are sufficiently high, the critical condition for initial exponential growth will be attained. High initial temperatures for the earth are predicted by the planetesimal accretion model.     

Rational modifications,synthesis and biological evaluation of new potential antivirals for RSV designed to target the M2-1 protein

Respiratory syncytial virus (RSV) is the main cause of lower respiratory tract diseases in infants and young children, with potentially serious and fatal consequences associated with severe infections. Despite extensive research efforts invested in the identification of therapeutic measures, no vaccine is currently available, while treatment options are limited to ribavirin and palivizumab, which both present significant limitations. While clinical and pre-clinical candidates mainly target the viral fusion protein, the nucleocapsid protein or the viral polymerase, our focus has been the identification of new antiviral compounds targeting the viral M2-1 protein, thanks to the presence of a zinc-ejecting group in their chemical structure. Starting from an anti-RSV hit we had previously identified with an in silico structure-based approach, we have designed, synthesised and evaluated a new series of dithiocarbamate analogues, with which we have explored the antiviral activity of this scaffold. The findings presented in this work may provide the basis for the identification of a new antiviral lead to treat RSV infections.     

Fitness Is Strongly Influenced by Rare Mutations of Large Effect in a Microbial Mutation Accumulation Experiment

Our understanding of the evolutionary consequences of mutation relies heavily on estimates of the rate and fitness effect of spontaneous mutations generated by mutation accumulation (MA) experiments. We performed a classic MA experiment in which frequent sampling of MA lines was combined with whole genome resequencing to develop a high-resolution picture of the effect of spontaneous mutations in a hypermutator (ΔmutS) strain of the bacterium Pseudomonas aeruginosa. After ∼644 generations of mutation accumulation, MA lines had accumulated an average of 118 mutations, and we found that average fitness across all lines decayed linearly over time. Detailed analyses of the dynamics of fitness change in individual lines revealed that a large fraction of the total decay in fitness (42.3%) was attributable to the fixation of rare, highly deleterious mutations (comprising only 0.5% of fixed mutations). Furthermore, we found that at least 0.64% of mutations were beneficial and probably fixed due to positive selection. The majority of mutations that fixed (82.4%) were base substitutions and we failed to find any signatures of selection on nonsynonymous or intergenic mutations. Short indels made up a much smaller fraction of the mutations that were fixed (17.4%), but we found evidence of strong selection against indels that caused frameshift mutations in coding regions. These results help to quantify the amount of natural selection present in microbial MA experiments and demonstrate that changes in fitness are strongly influenced by rare mutations of large effect.